The Uxpanapa-Chimalapa region covers c. 7700 km² in extreme south-eastern Veracruz and
eastern Oaxaca states (Map 13). The region includes the Atlantic
slope of the eastern portion of the Isthmus of Tehuantepec, mostly in the drainage of the
Coatzacoalcos River and its major tributary the Uxpanapa River, and extends from the Gulf
of Mexico lowlands southward to the highlands of the continental divide; a part of eastern
Chimalapa is in the Grijalva River drainage.

The Uxpanapa section (c. 2600 km²) includes the parts in Veracruz and in the
municipality of Matías Romero (the "Colonia Cuauhtemoc") in Oaxaca. The
Chimalapa section (c. 5100 km²) encompasses essentially all of the municipality of Santa
María Chimalapa and the gulf slope and highlands of the municipality of San Miguel
Chimalapa, both in Oaxaca; the southern boundary of the region is the southern boundary of
the montane forests of the Sierra Atravesada.

1. A karst area in northern Uxpanapa (pictures), with
relatively little macrorelief but numerous small to large limestone outcrops. Average
elevation 100-150 m.

2. An eastwest strip in central Uxpanapa, with deep, flat alluvial soils formed by
northflowing rivers and alluvial outwash from the mountains to the south. Average
elevation 100-130 m.

3. In southern Uxpanapa northern Chimalapa, an area of steep hilly terrain fringing the
Sierra de Tres Picos, with very deep soils, and the relief becoming gradually higher
toward the sierra.

4. The Sierra de Tres Picos (picture), a small granitic
system with a number of steepsided peaks reaching 1450 m, in north-central Chimalapa.

5. The eastwest Río del Corte Valley (Upper Coatzacoalcos River) in central Chimalapa.
The river is mostly at an elevation of 80-250 m, its tributaries going through a complexly
dissected central area with no major flats in the montane areas.

6. The Sierra Atravesada (or Sierra Niltepec) of southern Chimalapa, a major eastwest
range of mostly granitic and metamorphic substrates, which forms the continental divide
and includes peaks such as Cerro Azul (the highest - 2250 m) and Cerro Baúl (2050 m). Its
eastern part is drained by the Negro River, a tributary of the Grijalva River. This range
along with the Sierra de Tres Picos forms the north-western end of the Sierra Madre de
Chiapas (Wendt 1983).

7. The limestone Sierra Espinazo del Diablo of north-eastern Chimalapa and a small part
of extreme south-eastern Uxpanapa, reaching 1350 m.

Moist gulf winds moving south across the Isthmus of Tehuantepec produce one of the
highest rainfalls in lowland Mexico in the Uxpanapa area. Average annual precipitation is
2800 mm in the west and 4400 mm in the east (Comisión del Papaloapan, unpublished). Even
higher rainfalls probably occur in the relatively unknown Sierra de Tres Picos. To the
south (leeward) of this range in Chimalapa, the precipitation in the Río del Corte
lowlands is less than in Uxpanapa, probably mostly 2000-3000 mm or less in some areas, and
greatest in the lower (western) part of the valley. The higher portions of the Sierra
Atravesada and Sierra Espinazo del Diablo are clearly very wet (but without records).

Rain is seasonal, with a marked dry season from March through May, when monthly
rainfall averages 60-100 mm in Uxpanapa. The wettest months are June to October. The
Uxpanapa area forms the western end of a roughly crescent-shaped lowland of high
precipitation ("the crescent area") that extends eastward in Mexico to southern
Tabasco and northern Chiapas (Wendt 1983, 1989, 1993).

Average annual temperature in the lowlands is 24°-25°C; monthly average temperatures
vary from around 20°C in January (and as low as 8°-10°C at night), to above 28°C in
May. Daytime temperatures can exceed 41°C (Comisión del Papaloapan, unpublished). The
highlands are cooler, but frosts appear to be rare and snow unknown.

The Uxpanapa-Chimalapa region includes the only major remaining well-developed rain
forest in Mexico apart from the larger but much more disturbed Lacandon forest of Chiapas
(Ewell and Poleman 1980) (CPD Site MA1, see Data Sheet). On the
lowland and hill areas of Uxpanapa and northern Chimalapa are evergreen and semi-evergreen
tropical rain forests, which vary according to the substrate (Wendt, unpublished):

3. Forest of the central Uxpanapa alluvial plain - almost completely
destroyed, its original composition is not well known. It appears to have been more
similar to the hill forest, with Ceiba pentandra, Dialium guianense, Terminalia
amazonia and Vochysia guatemalensis important.

4. Riparian forest - the most common tall trees are Ficus insipida
and Ocotea uxpanapana.

The Chimalapa area is notable for its very large tracts of undisturbed and little
disturbed lowland and montane forests; especially, there are large transects of
undisturbed lowland rain forest to montane cloud forest. The hill and riparian forests of
Uxpanapa extend into the Chimalapa area. Hill forest is widespread in the lower Río del
Corte Valley and areas near the Sierra de Tres Picos and Sierra Atravesada. The lower
elevations of the dissected topography of the central Río del Corte Valley support a
complex mixture of lowland oak forest (Quercus oleoides and other oaks), pine
forest (Pinus oocarpa), tropical rain forest, and semi-deciduous tropical forest,
with some elements of montane mesic forests (e.g. Liquidambar styraciflua, Pinus
chiapensis); this mixture, all at less than 600 m, is perhaps unique in Mexico. Very
small areas of rock outcrop near the river support unique xeric vegetation including
species of Agave, Beaucarnea and Yucca.

Montane areas of the Sierra de Tres Picos and Sierra Atravesada support diverse cloud
forests, which may represent the largest area of undisturbed cloud forest in Mexico and
Central America. These are isolated from other cloud forests of Oaxaca, Veracruz and
Chiapas by lower and/or drier intervening areas. Among the genera of canopy trees with one
or more common species are Alfaroa, Billia, Cedrela, Clethra, Genipa,
Inga, Liquidambar, Magnolia, Matayba, Oreomunnea, Pinus,
Podocarpus, Quercus, Ticodendron and Weinmannia, along with
numerous species of Lauraceae. Elfin forest occurs along the crest of the Sierra de Tres
Picos and on some peaks of the Sierra Atravesada. Extensive pine forests with Pinus
oocarpa and other pines are found in the lower, eastern Sierra Atravesada. The montane
forests of the Sierra Atravesada become drier south of the continental divide and give way
to tropical deciduous forest at lower elevations on the Pacific slope (beyond our region).

The first collections in the Uxpanapa area were those in the early 1970s by the Flora
de Veracruz project (cf. Márquez-Ramírez, Gómez-Pompa and Vázquez-Torres 1981),
except for some in the 1930s along the Coatzacoalcos River in the west. Since 1980, the
Colegio de Postgraduados, Chapingo, has had an intensive collecting programme (MacDougall
1971; Myers 1980; cf. Wendt 1987). The Uxpanapa lowlands are now relatively well known;
over 200 species of canopy trees have been recorded. The entire region is estimated to
have 3500 vascular plant species.

Wendt (1989) reported on the high endemism of the Uxpanapa flora (including northern
Chimalapa), and proposed the area as a refuge for rain-forest species during cycles of
climatic deterioration during the Pleistocene and earlier. His partial lists include at
least 36 species apparently endemic to the Uxpanapa area and 11 more endemic to the high
precipitation crescent area. Many other species are known in Mexico only from this area.
Wendt (1993) has shown that the Uxpanapa area is perhaps the most important centre for
endemism in canopy trees of the Mexican rain forest.

Several genera and one family are known in Mexico only from Uxpanapa-Chimalapa (Wendt
1988, 1989), and more genera are known only from the crescent area (cf. Wendt 1993).
Noteworthy rain-forest trees include the monotypic genus Chiangiodendron, abundant
only in Uxpanapa (although also known from Chiapas) and the only New World member of its
tribe (Wendt 1988); Eschweilera mexicana (endemic to Uxpanapa-Chimalapa), the only
representative of the Lecythidaceae in Mexico (Wendt, Mori and Prance 1985); many other
endemic canopy tree species including Ocotea uxpanapana, Sterculia new sp. (picture) and Tapirira chimalapana; two new flagelliflorous
understorey species of Annonaceae, one of which appears to be a new genus (Schatz and
Wendt, unpublished); and a new understorey genus of Rutaceae (Chiang, unpublished). All of
the canopy trees just mentioned are very common to co-dominant elements of the rain
forests of the region. A number of other abundant canopy trees are more widespread, but
restricted in Mexico to Uxpanapa-Chimalapa (e.g. Pouteria torta subsp. tuberculata).

The Chimalapa area had been only sporadically collected (MacDougall 1971) until the
Colegio de Postgraduados, Chapingo, began intensive collecting in 1984. However, due to
the very remote nature of most of the area and its great vegetational diversity, it
remains poorly known floristically. Its rain forests are mostly similar to the Uxpanapa
hill forests and share many of their unique species. The montane forests include many
species also known from the Sierra de Juárez of northern Oaxaca (CPD
Site MA3, see Data Sheet) and the cloud forests of Chiapas, but already have yielded a
number of new species in both the tall forests and elfin forests. The Oreomunnea
forests are probably better developed in Chimalapa than in any other part of Mexico, and
as well as less disturbed. Preliminary studies of the xerophytic outcrop vegetation near
El Corte River indicate high endemism in its small flora.

The region contains important timber resources, including not only such widespread high
quality tropical woods as Cedrela odorata (tropical red-cedar), Calophyllum
brasiliense var. rekoi (Santa María) and Swietenia macrophylla (bigleaf
mahogany), but important endemics such as the new, undescribed species of Sterculia,
which has been much used locally in the manufacture of fine plywood. Furthermore, a large
native population of the important fruit tree Pouteria sapota (the "zapote
mamey") is present; there are few such populations elsewhere. Several non-timber
montane species are important in the local economy, especially "palmita" (Chamaedorea
sp.), the leaves of which are carefully harvested without killing the plant, and sold for
ornamental purposes. Caballero et al. (1978) emphasize the usefulness to local
peoples of a large proportion of the native Uxpanapa species. The endemic species still
include many that have never been investigated for possible uses, since the region was
virtually uninhabited until the past few decades.

The Uxpanapa-Chimalapa region is one of the most important remaining natural areas in
Mexico for wild animals. There are large populations of such threatened species as jaguar
and Baird's tapir, together with spider monkeys, tayra, agouti, kinkajou and many others.

Birds include the northernmost population of quetzal, large populations of curassow,
and many others; harpy eagles have been reported in the Chimalapa area. There are no
Endemic Bird Areas (EBAs) in the region, but the whole range of the highly localized and
threatened Nava's wren (Hylorchilus navai) is restricted to karst forest in
Uxpanapa and immediately adjacent Chiapas; the entire genus Hylorchilus is endemic
to the Mexican karst rain forest (Atkinson et al. 1993).

The montane forests of the Sierra Atravesada contain a biogeographically distinctive
herpetofauna with a significant endemic component; Campbell (1984) states that this range
represents "a pivotal point of major importance in the distribution of Middle
American cloud-forest reptiles and amphibians" - yet most of the range remains
herpetologically unknown.

Uxpanapa and Chimalapa form the headwaters of the Coatzacoalcos River drainage, which
has important downstream cities (Coatzacoalcos, Minatitlán) where flooding has increased
since development of the Uxpanapa area began. Adequate forest and rational management are
essential for control of soil erosion, flooding and water quality, especially considering
the steep fragile soils of southern Uxpanapa and northern and eastern Chimalapa.

The region has potential for tourism, especially with regard to the animals, the
beautiful rock formations and flora of the karst zone, and the true wilderness quality of
much of Chimalapa.

Uxpanapa did not support a large indigenous population, and except for logging
operations and other development near the Coatzacoalcos River (Río del Corte) in the
west, it was almost completely undeveloped and unsettled until the early 1970s, when the
federal government (Comisión del Papaloapan) started a major project in the Veracruz
portion of Uxpanapa to resettle indigenous Chinanteco people displaced by the Cerro de Oro
dam. Huge areas were cleared mechanically, mostly on the deep flat soils of the central
part, but including some karst areas completely unsuited for agriculture or livestock.
Early large-scale agricultural schemes (notably with rice) were conspicuous failures
(Ewell and Poleman 1980), although many areas proved suitable for smaller scale
subsistence agriculture. Large areas of closer hill forest were burned by escaped
"milpa" fires during spring; some was converted into pasture. There also have
been incursions into the bordering Chimalapa forests.

By 1980, perhaps one-half of the Uxpanapa area still supported primary forest. During
the 1980s, the attrition rate in the Veracruz part of the area was slower, due to the
limited number of settlers allowed, a partially enforced statewide ban on cutting of
primary forest, and the fact that the prime agricultural lands had already been cleared
(cf. Wendt 1993). However, logging in the Colonia Cuauhtemoc area in Oaxaca has
intensified, often including part of the Chimalapa area and advancing toward the Sierra de
Tres Picos. Large tracts of forest are subsequently cleared for agriculture, grazing and
colonization.

The Comisión del Papaloapan in the 1980s developed a master plan for the Veracruz
part; included were areas designated for forestry and for biotic reserves. Many karst
areas and hill areas with extreme slopes were not to be developed. However, the Veracruz
part went completely into State responsibility in 1985; its future is unclear. The karst
forests are less threatened at present due to the difficulty of logging and the low
agricultural potential of their soils. However, the rich hill forests in both Veracruz and
Oaxaca have, as of 1995, almost vanished.

The history of the Chimalapa area has been quite different. Since pre-Hispanic times
the Chima (a small Zoque population) have been there, centred in the area of the present
town of Santa María Chimalapa. The Chimas communally own all of the municipality of Santa
María Chimalapa, but the right to use parcels of the land may not only be inherited but
bought, including by outsiders who are accepted as "comuneros". A similar
situation pertains in the south-eastern portion of the area for some communal lands of San
Miguel Chimalapa.

Before the 1970s, the only significant impact was near the town of Santa María and a
few small areas westward, and along the Chiapas border to the east. Since then, logging,
agriculture and/or settlements have increased westward and along the borders with Veracruz
and Chiapas. As of 1995, only the vast heart of the Chimalapa area - Sierra de Tres Picos,
upper Río del Corte Valley, much of the Sierra Atravesada - remains little disturbed and
completely without roads. However, several large-scale developments have been proposed,
including major dams on El Corte River and its tributaries as part of an irrigation scheme
for the southern dry side of the Isthmus of Tehuantepec, and also major internationally
financed forestry projects. A proposed second trans-isthmian highway to connect the area
of Acayucán, Veracruz with Cintalapa, Chiapas would cut diagonally across Uxpanapa and
north-eastern Chimalapa, further threatening the region due to concomitant colonization.

For the Uxpanapa area, no official plan for conservation exists. Before the dissolution
of the Comisión del Papaloapan, the agency's field personnel in Uxpanapa were much
interested in the possibility of parks and tourism to boost the local economy and protect
the watersheds. Nevertheless, presently there appears to be no effort within the
government to establish parks or to preserve part of the area.

There has, however, been much interest in the future of the Chimalapa area within the
now vigorous Mexican conservation community, including the formation in 1991 of a National
Committee for the Defense of the Chimalapas. Interest thus focused has led to increased
appreciation by local people for the unique nature of the area, international support for
studies of the zone, an attempt to solve boundary disputes and encroachments, and a
government proposal for a Biosphere Reserve, which however is opposed by the local
populace and some conservation groups. Although details are still sketchy, present plans
made with greater local input call for a "campesino"-administered Biological
Reserve.